The present invention relates to an optical information recording/reproducing apparatus and an optical information recording/reproducing method for recording or reproducing optical information data on or from an optical recording medium by using a two-group objective lens having an increased numerical aperture.
In an apparatus for recording or reproducing optical information on or from an optical recording medium, a spot size xe2x80x9cdxe2x80x9d on the recording medium is expressed by the following equation:
d=xcex/NAxe2x80x83xe2x80x83(1)
In this equation, xcex is the wavelength of a light beam and NA is a numerical aperture of an objective lens.
As is apparent from the equation (1), the shorter the wavelength xcex of a light beam emitted from a light source becomes and/or the larger the numerical aperture NA of an objective lens becomes, the smaller the spot side xe2x80x9cdxe2x80x9d becomes. The reduction of the spot size xe2x80x9cdxe2x80x9d enables high density recording of optical information.
It is known that the use of an aspherical two-group objective lens is effective to make large the numerical aperture of an objective lens which is one of the above factors to reduce the spot size xe2x80x9cdxe2x80x9d. Japanese Patent Laid-open No. Hei 9-251645 (Japanese Patent Application No. Hei 8-58870) by the present top inventor and the present applicant discloses an apparatus and a method for recording or reproducing optical information on or from a recording medium using a two-group objective lens, characterized by suppressing occurrence of spherical aberration.
In the case of using such a two-group objective lens, to obtain the best reproducing signal from a recording medium, it is required to optimize a distance between lenses constituting the two-group objective lens for minimizing wavefront aberration. Japanese Patent Application No. Hei 8-340903 made by the present first inventor and the present applicant discloses an apparatus and a method for recording/reproducing optical information on or from an optical disk. In this document, an optical disk drive using an optical head having a two-group objective lens is configured such that lenses constituting the two-group objective lens are integrally moved for focus servo operation and then the tail spherical lens of the two-group objective lens is independently moved in the direction of the optical axis to minimize wavefront aberration.
The R.M.S (route mean square) value of the wave front aberration should be preferably less than xcex/14.
A focal depth (fd) defined by NA and xcex is expressed by the following equation:
fd=xcex/NA2xe2x80x83xe2x80x83(2)
As is apparent from the equation (2), in the case of using an objective lens with a high numerical aperture, the focal depth fd is significantly reduced. For example, the focal depth fd of a two-group objective lens having a numerical aperture NA of 0.85 is reduced to about half that of an objective lens (numerical aperture NA: 0.6) of an optical disk drive used for a DVD (Digital Video Disk)-RAM (Random Access Memory).
Accordingly, in the case of using an objective lens with a high numerical aperture, more accurate focus control is required to be performed sufficiently to follow a change in environmental temperature, a change with elapsed time, and the like. Japanese Patent Application No. Hei 9-84090 made by the present top inventor and the present applicant discloses a focus control device and a method thereof, and an optical disk drive using an optical head having a two-group objective lens with a high numerical aperture, in which focus control is accurately performed by optimizing the servo offset in focus servo, to thereby obtain the best reproducing signal from an optical disk.
Since the distance between lenses of a two-group objective lens and the servo offset in focus servo are both optimized on the basis of the same reproducing signal from a recording medium, it is required to establish a method capable of simultaneously optimizing both the above distance between lenses and servo offset. Also it is required to optimize the position of each lens before recording is started. Further, in the case of an unrecorded medium, the above optimization must be performed using pre-formatted embossed pits or the like.
The above-described related art methods, however, have problems. Namely, although the distance between lenses of a two-group objective lens and the servo offset in focus servo must be simultaneously optimized because they are optimized on the basis of the same reproducing signal from a recording medium, the above related art methods do not consider any method of simultaneously optimizing both the distance between lenses and servo offset.
In the case of a unrecorded medium, it may be considered to perform the above optimization using preformatted embossed pits or the like; however, since these pits are generally, discretely formed on a recording medium, there occurs an inconvenience that it is difficult to perform the above optimization using continuous reproducing signals.
An object of the present invention is to provide an optical information recording/reproducing apparatus and an optical information recording/reproducing method, which are capable of simultaneously optimizing a distance between lenses of a two-group objective lens and an offset value in focus control.
To achieve the above object, according to a first aspect of the present invention, there is provided an optical information recording/reproducing apparatus including an optical pickup for making a light beam emitted from a light source incident on a recording medium via a two-group objective lens so as to record or reproduce optical information on or from the recording medium, the two-group objective lens including a first lens disposed in the vicinity of the recording medium and a second lens disposed at a position facing to the recording medium with the first lens put therebetween, the apparatus including: a moving means for cyclically moving at least one of the first lens and the second lens constituting part of the optical pickup in the direction of the optical axis thereof; and a control means for performing, upon focusing operation, the positional adjustment of the first lens and the second lens after start-up of focus control, on the basis of reproducing signals obtained from the recording medium at one or more points of the cyclic movement of the at least one of the first lens and the second lens by the moving means.
According to a second aspect of the present invention, there is provided an optical information recording/reproducing apparatus including an optical pickup for making a light beam emitted from a light source incident on a recording medium via a two-group objective lens and at least a third lens so as to record or reproduce optical information on or from the recording medium, the two-group objective lens including a first lens disposed in the vicinity of the recording medium and a second lens disposed at a position facing to the recording medium with the first lens put therebetween and being configured such that a distance between the first lens and the second lens is fixed, the apparatus including: a first drive means for integrally driving the first lens and the second lens in the direction of the optical axis thereof, and a second drive means for driving the third lens in the direction of the optical axis thereof; a moving means for cyclically moving at least one of the first and second lenses and the third lens constituting part of the optical pickup in the direction of the optical axis thereof; and a control means for performing, upon focusing operation, the positional adjustment of the first and second lenses and the third lens after start-up of focus control, on the basis of reproducing signals obtained from the recording medium at one or more points of the cyclic movement of the at least one of the first and second lenses and the third lens by the moving means.
According to a third aspect of the present invention, there is provided an optical information recording/reproducing apparatus including an optical pickup for making a light beam emitted from a light source incident on a recording medium via a primary lens disposed in the vicinity of the recording medium and at least a secondary lens so as to record or reproduce optical information on or from the recording medium, the apparatus including: a first drive means for driving the primary lens in the direction of the optical axis thereof, and a second drive means for driving the secondary lens in the direction of the optical axis thereof; a moving means for cyclically moving at least one of the primary lens and the secondary lens constituting part of the optical pickup in the direction of the optical axis thereof; and a control means for performing, upon focusing operation, the positional adjustment of the primary lens and the secondary lens after start-up of focus control, on the basis of reproducing signals obtained from the recording medium at one or more points of the cyclic movement of the at least one of the primary lens and the secondary lens by the moving means.
According to a fourth aspect of the present invention, there is provided an optical information recording/reproducing method which is carried out by using an optical pickup for making a light beam emitted from a light source incident on a recording medium via a two-group objective lens so as to record or reproduce optical information on or from the recording medium, the two-group objective lens including a first lens disposed in the vicinity of the recording medium and a second lens disposed at a position facing to the recording medium with the first lens put therebetween, the method including the steps of: cyclically moving at least one of the first lens and the second lens constituting part of the optical pickup in the direction of the optical axis thereof; and performing, upon focusing operation, the positional adjustment of the first lens and the second lens after start-up of focus control, on the basis of reproducing signals obtained from the recording medium at one or more points of the cyclic movement of the at least one of the first lens and the second lens by the moving means.
The function of the optical information recording/reproducing apparatus and optical information recording/reproducing apparatus of the present invention will be described below.
First, an offset value in focus control and a distance between lenses of the two-group objective lens are set at pre-set values. Then, sine wave drive signals are applied to the moving means to cyclically, slightly move the first and second objective lenses in the direction of the optical axis.
A low band component of a change in amplitude, that is, an envelope component of a reproducing signal is detected, and is decided whether the amplitude obtained when the distance between the first and second lenses is minimized is larger or smaller than the amplitude obtained when the distance between the first and second lenses is maximized. If larger, the distance between the first and second lenses of the two-group objective lens is smaller than the optimum value. In this case, control is performed to increase the distance between the first and second lenses.
If the amplitude obtained when the first objective lens becomes closest to the recording medium is smaller than that obtained when the first objective lens becomes remotest from the recording medium, the distance between the first and second lenses of the two-group objective lens is larger than the optimum value. In this case, control is performed to decrease the distance between the first and second lenses.
Next, an operational mode of the optical disk drive is decided. If the drive receives a recording command, the distance between the lenses of the two-group objective lens is fixed and the application of the sine wave drive signals to the moving means for moving the first and second lenses is stopped, and recording is started.
Further, a high band component of the envelope component of a reproducing signal is detected, and it is decided whether the amplitude obtained when the first and second lenses become closest to the recording medium is larger or smaller than the amplitude obtained when the first and second lenses become remotest from the recording medium. If larger, the signal plane is remoter from the optical disk drive than the focus position is. In this case, control is performed to increase the focus bias value.
If the amplitude obtained when the first and second lenses become closest to the recording medium is smaller than the amplitude obtained when the first and second lenses become remotest from the recording medium, the signal plane is closer to the optical disk drive than the focus position is. In this case, control is performed to decrease the focus bias value.
Next, an operational mode of the optical disk drive is decided. If the drive receives a recording command, the focus bias value is fixed and the application of the sine wave drive signals to the moving means for moving the first and second lenses is stopped, and recording is started.